Drawbars are typically used to semi-permanently connect units of rail cars together as a single long train of cars when the cars have a fixed-use application such as transporting coal, ore, grain and the like, the units usually being comprised of five or ten cars per set. In those types of applications, drawbars replace conventional E and F type couplers which are used to detachably couple cars that have a single unit application.
More particularly, rotary drawbars permit multiple unit commodity trains to be emptied at an unloading station by rotating the entire car while it remains connected to the next awaiting car. The full-car dump practice is accomplished by using a drawbar connecting arrangement where the cars in each unit set have a fixed end connection on one end of the drawbar and a rotary connection on the other end. This type of car coupling arrangement alternates between each successive car in the unit. The rotatable coupling connector can either be a typical spherically shaped butt end head or it can be a standard F type coupling member with rotational capabilities. The fixed end is typically a vertically or horizontally pinned standard drawbar butt head. The prior art is replete with the various types of drawbar arrangements having different types of butt end heads, the drawbars almost invariably being of the slackless type. Variations of the types of slackless drawbars described above are illustrated in U.S. Pat. Nos. 5,000,330, 4,700,854, 4,593,827, 4,580,686, 4,456,133, 4,420,088. None of these patents disclose the principles of the present invention.
In the unloading process, an on-site rail car indexer and positioner electronically senses or indexes the car coupling device and then, depending upon the specific area of the coupling the indexer is programmed to encounter, positions an index mounted pusher arm for embracement with a designated point on the car coupling arrangement. Once embraced, the indexing car moves the entire car unit towards the unloading station, the first car in the unit being placed in the correct unloading position on the dumping platform. Because a drawbar shank does not have the structural coupling head features of E and F type couplers, drawbar shanks must be cast with generic E and F coupling head features so that the indexer can be tricked into thinking it has located and indexed a type E or F coupler head for purposes of setting the pusher arm. In this way, an entire train of cars can be unloaded without requiring the entire train of cars to use the same type of coupling heads.
When the cars are utilizing other unloading schemes such as bottom dump cars in combination with shakeout houses, the drawbar coupling arrangement of each unit usually consists of cars coupled together with both ends fixed by either vertically or horizontally pinned arrangements like those found in U.S. Pat. No. 4,700,853 or U.S. Ser. No. 568,773, allowed Oct. 21, 1991.
One problem common to all drawbars is that most of their connection parts are cast as either a single casting integral with the drawbar itself, or because of their complexity, are cast as separate coupling members from the main drawbar intermediate section, and are later welded together. Furthermore, the long, slender shape of a single integral casting is not an optimum shape to produce since casting is an expensive method of manufacturing. Another problem facing drawbar manufacturers is that railcar manufacturers are building longer cars due to economic reasons associated with hauling. The longer cars require drawbars of longer lengths to safely allow successful horizontal cornering of the car or else the probability of derailment is greatly increased. The longer drawbars can become a manufacturing problem for the suppliers because the overall drawbar length may exceed the flask capacity of a particular manufacturer's operation. The flask capacity is the volumetric size of the casting tundish. If the tundish cannot hold the amount of molten metal needed to cast the longer drawbars, it cannot be made, creating lost opportunities. Furthermore, even if a supplier has adequate flasking capacities, each time a new drawbar of a different length is made, a new casting mold must also accompany the new length. This aspect of manufacturing an entirely cast drawbar of varying lengths makes the casting process extremely expensive. Nevertheless, because of the high costs associated with casting even the standard length drawbar arrangements, the drawbar is a high cost item of a railcar underframe.
On the otherhand, casting of drawbars and coupling systems does have one main advantage over fabrication, namely, the ability to more easily produce the complex end pieces, whether they are special butt end heads or F-type butt end heads.